Unlicensed mobile access generally describes the accessing of public land mobile networks using access networks that utilise a typically low-power unlicensed-radio interface to communicate with mobile stations. Existing access networks typically include broadband networks that may include both wireless and wired portions, preferably IP networks, such as wireless LANs, in which higher layer protocols, such as the GSM protocols, are run over an IP network rather than over the associated GSM radio layer. An access network controller communicates over the IP network with mobile stations that are connected to the network via access points. The access network controller also controls the interface with the public mobile network core elements that provides specific services to the mobile stations depending on the type of the public mobile core network. A security gateway also forms part of the access network and is either combined with the access network controller in a single node or implemented as a separate node. Access networks of this type have been used to provide access to second generation PLMNs including GSM (Global System for Mobile Communication), EDGE (Enhanced Data rates for GSM Evolution) and GPRS (General Packet Radio Service networks), which are often grouped under the term GSM/EDGE radio access networks or GERAN. In this context, unlicensed access networks are referred to as generic access networks (GAN) and the access network controller is called a generic access network controller or GANG. Work is now ongoing in 3GPP for Release 8 to specify generic access networks for third generation services UMTS (Universal Mobile Telecommunications System) or WCDMA (Wideband Code Division Multiple Access). The corresponding technical specifications will be called 3GPP TS 43.319 and 44.319 and will also include the previous content from specifications 43.318 and 44.318 in 3GPP Releases 6 and 7
In the case of both second and third generation public mobile networks the generic access networks are designed to communicate directly with the core elements of a standard public mobile network. The generic access network is constructed so that the core network elements, such as the mobile switching centers MSC of the public mobile network, view the access network as a conventional base station BSS or radio network controller RNC. In the present GAN standard, this is achieved by constraining the GANG to use second generation GSM interfaces towards the core network. In other words, the GANG communicates via the A-interface with mobile services switching centers MSC for circuit-switched services and via the Gb-interface with Serving GPRS support nodes (SGSN) for packet-switched services. For third generation mobile networks it is proposed that the GANG should use WCDMA/UMTS interfaces towards the mobile core network, i.e. an Iu-cs interface towards the mobile services switching center MSC for circuit-switched services and Iu-ps interface towards the serving GPRS support node (SGSN) for packet-switched services. It is further envisaged that some generic access network controllers will use both second and third generation interfaces towards the core network elements, and hence be capable of supporting the services of both network types. The interfaces used between the access network controller and core network determine which services and the performance for some services that can be delivered to the mobile stations.
Mobile stations capable of using a generic access network support a wireless IP access technology, such as Bluetooth or Wi-Fi, in addition to GERAN radio interfaces and hence are capable of operating in either generic access network mode (GAN-mode) or GERAN-mode. Such a terminal may additionally support UNITS terrestrial radio access network interfaces (UTRAN interfaces) and hence offer three modes of operation. When the mobile station wants, or needs, to switch from GERAN/UTRAN mode to GAN-mode operation, i.e. to use a generic access network rather than the public mobile access network to access core network services, it must first register with a generic access network controller GANC that serves its current location. Since the mobile station may not have the necessary address information stored it will first register with a default GANC, which is located in the public land mobile network to which the mobile station subscribes, also known as the home public land mobile station HPLMN. The mobile station thus sends a register request message to the default GANC, and the message includes an indication of the current location of the MS in the form of the identity of the serving cell. If the default GANC is unable or unwilling to serve the mobile station in this location based, for example, on network configuration operator policies, it will redirect the mobile station to another GANC within the same PLMN or even present a choice of GANCs that are associated with different PLMNs by sending a GAN PLMN list in accordance with the mentioned 3GPP standards.
A problem with the registration process within the generic access network is that the end user is unable to select a specific service when presented with a choice of PLMN-GANC pairs. In other words, whilst a specific PLMN may offer both second and third generation services over the generic access network, the end user has no means of knowing which of these services is supported by a specific serving GANC included in the GAN PLMN list.
It is thus an object of the present invention to improve the transparency of the registration process within an unlicensed access network.
It is a further object of the present invention to improve the registration process to provide the necessary service information to enable the end user or the mobile station to exercise an informed choice when selecting unlicensed access to a public land mobile network.